Multiple-input multiple-output (“MIMO”) antennas provide better performance in terms of data rate and reliability, as compared to single antenna systems. Therefore, MIMO antennas are typically desirable for in-building communication systems. However, making such MIMO antennas with relatively small dimensions, and particularly with a low profile, can be challenging. One challenge is achieving adequate isolation between multiple, co-located transmit and receive antennas of the MIMO antenna. Ultra-wideband (“UWB”) performance to cover an entire desired frequency range (e.g., all commercial communication and data bands between 700-2700 MHz) is another major challenge. Further, designing MIMO antennas that combine the benefits of UWB and low coupling between multiple, co-located antennas (i.e., highly-isolated antennas) can prove even more difficult.